The present invention relates to the technology of image recording apparatus using a long line head. More particularly, the present invention relates to a line head that is composed of an array of short heads and can be manufactured easily at a low cost and to an image recording method capable of recording an image of high quality using this line head.
Unexamined Published Japanese Patent Application JP, 48-009622, A and JP, 54-051837, A teach inkjet recording apparatus of a type in which part of ink is rapidly evaporated by impulse heating so that the resulting force of expansion allows ink drops to be propelled from orifices.
JP, 05-050601, A and JP, 11-207956, A teach inkjet recording apparatus of another type in which a diaphragm is provided in an ink chamber and vibrated by static electricity, with a piezoelectric device or otherwise so that ink drops are propelled from nozzles. These and other types of inkjet recording apparatus have many advantages such as fairly low price, ease in handling and good image quality and hence are used extensively as printers in various applications.
In such inkjet printers and various other printers that employ a xe2x80x9crecording headxe2x80x9d as in thermal printers and dot impact printers, the recording head is usually a short one comprising an array of recording elements and the recording medium at rest is scanned by the recording head which is moved by a carriage in a direction which is approximatelly or substantially perpendicular to the direction of arrangement of the recording elements and when one scan cycle ends, the recording medium is moved in the direction of arrangement of the recording elements over the distance determined by the number of recording elements in the head and another scan is performed by the same procedure as described above; this process is repeated to record image on the entire surface of the recording medium.
Printers are also known that use a so-called xe2x80x9cline headxe2x80x9d which has recording elements arranged over a distance to cover the entire length of one side of the recording medium.
The major advantage of using the line head is that by merely performing relative movements (scanning) of the recording medium and the Line head in an auxiliary direction (auxiliary scanning direction) substantially perpendicular to the direction of arrangement of the recording elements, the entire region of the recording medium can be scanned with the recording elements to record image on the entire surface of the recording medium. As a result, printers using the line head can accomplish image recording rapidly and by simple operations without movement of the carriage and intermittent transfer of the recording medium.
On the other hand, the line head has several disadvantages such as higher cost, lower yield and reliability than the short head. In addition, if some of the recording elements break, the expensive line head has to be replaced as a unit and this results in high repair cost.
In order to solve these problems of the line head, it has been proposed that a plurality of short heads each having recording elements arranged in one direction (a main scanning direction) be arranged in the main scanning direction (see Examined Japanese Patent Publication JP, 4-038589, B) The advantages of short heads such as low cost, high yield and reliability are retained by this line head. In addition, if some recording elements break, only the short head having such broken recording elements need be replaced and this contributes to considerable economy in terms of repair cost.
On the other hand, in order to ensure that high-quality image without defects such as streaks (streaky unevenness in density or concentration) and clear spots is recorded with the line head comprising an array of short heads, the individual short heads must be positioned exactly enough to give an appropriate or equal pitch of recording elements at each of the joints between adjacent short heads. It goes without saying that the ends of adjacent two short heads which form the joint therebetween need be produced in an extremely precise manner so that the short heads can be positioned exactly.
However, the recording elements are arranged at such small intervals (e. g. on a pitch of 20 xcexcm if the resolution is 1200 dpi) that difficulty is found in arranging many short heads in exact registration in terms of making the end of each short head which forms a joint with that of the adjacent short head, and considerable difficulty is involved in positioning.
A first object of the present invention, which solves the above-described problems of the conventional art, is to provide a line head for use in recording an image by inkjet and the like which is composed of a plurality of short heads each having recording elements arranged in one direction and capable of easily performing an arrangement or a registration of the short heads whereby a manufacturing process can be simplified and a cost reduction can be realized.
Further, a second object of the present invention is to provide an image recording method capable of recording an image of high quality without unevenness in color, density (concentration) and the like by using the above-described line head.
In order to achieve the above-described first object, the first aspect of the present invention provides a line head, comprising: a plurality of short heads, each of which has an array of recording elements arranged in one direction, disposed in the one direction of arrangement, wherein two of the plurality of short heads which are adjacent to each other in the one direction of arrangement are located at different positions from one another in an auxiliary scanning direction which is approximately or substantially perpendicular to the one direction of arrangement, and wherein an interval between a recording element of one of the two of the plurality of short heads and a recording element of the other short head, which two recording elements are adjacent to each other in the one direction of arrangement when viewed from the auxiliary scanning direction, is equal to or less than an arrangement pitch of the array of the recording elements in the two of the plurality of short heads; further comprising: a selection unit for selecting the recording elements to be used in a joint region of two of the plurality of short heads which are adjacent each other in accordance with the arrangement pitch of the array of the recording elements and the interval.
Preferably, in the line head of the first aspect, the two of the plurality of short heads which are adjacent to each other in the one direction of arrangement are located such that respective arrays of the recording elements are partly overlapped with each other when viewed from the auxiliary scanning direction.
In the case of recording one line to be recorded on a recording medium by employing a line head comprising a plurality of short heads that are arranged such that the arrays of recording elements of two of the short heads adjacent to each other are partly overlapped with each other as above, it is preferable to shift recording timings by a period of time which is determined depending on the distance in the auxiliary scanning direction between recording elements of two short heads adjacent to each other as well as the auxiliary scanning speed so that arrays of recording elements of a plurality of short heads ray effect recording in one and the same line to be recorded.
Preferably, each of the plurality of short heads comprises a plurality of rows of arrays of the recording elements in the auxiliary scanning direction.
Preferably, a plurality of head units in each of which the plurality of short heads are arranged in the one direction of arrangement are arranged in the auxiliary scanning direction.
In order to achieve the above-described second object, the second aspect of the present invention provides a method of recording an image on a recording medium employing a line head, the line head comprising a plurality of short heads, each of which has an array of recording elements arranged in one direction, disposed in the one direction of arrangement, wherein two of the plurality of short heads which are adjacent to each other in the one direction of arrangement are located at different positions from one another in an auxiliary scanning direction which is approximately or substantially perpendicular to the one direction of arrangement, and wherein an interval between a recording element of one of the two of the plurality of short heads and a recording element of the other short head, which two recording elements are adjacent to each other in the one direction of arrangement when viewed from the auxiliary scanning direction, is equal to or less than an arrangement pitch of the array of the Recording elements in the two of the plurality of short heads, comprising the steps of: moving relatively the line head and the recording medium in the auxiliary scanning direction; and driving the recording elements while controlling the driving each of the recording elements in a joint region of two of the plurality of short heads which are adjacent to each other in the line head in accordance with the arrangement pitch of the array of the recording elements and the interval.
Preferably, the driving step comprises the step of: controlling the driving of the recording elements of at least one of the two of the plurality of short heads in the joint region in accordance with the interval such that unevenness in density caused by a difference between the interval and the arrangement pitch of the recording elements is corrected.
Preferably, the driving step further comprises the steps of: determining a position of a join, at which the driving of respective recording elements of each of the two of the plurality of short heads which are adjacent to each other is switched from one short head to the other short head, between the recording element of the one short head and he recording element of the other short head, which the two recording elements are adjacent to each other in the one direction of arrangement; controlling the driving of the recording elements of at least one of the short heads in accordance with the interval in the position of the joint such that the unevenness in density caused by a difference between the interval and the arrangement pitch of the recording elements is corrected.
Preferably, the driving step comprises the step of: stopping use of the recording element which exists in a side of an end of each of the two of the plurality of short heads from the recording element of the one short head or the recording element of the other short head, the latter two recording elements being adjacent to each other in the one direction of arrangement and determining the position of the joint.
Preferably, the position of the joint is changed while the image is recorded.
Preferably, when each of the plurality of short heads has a plurality of rows of arrays of the recording elements in the auxiliary scanning direction, the position of the joint is changed based on an array of the recording elements.
Preferably, when each of the plurality of short heads has a plurality of rows of arrays of the recording elements in the auxiliary scanning direction, the position of the joint is changed in accordance with recording timing of the recording elements.
Preferably, the controlling of the driving of the recording elements is performed by at least one method selected from the group consisting of: control of recording dot density, control of recording density and control of an area of one recording dot.
That is, it is preferable to control the drive of the recording elements by controlling at least one of a recording dot (or pixel) density, a recording (color) density (concentration), and the area of one recording dot.
Preferably, the two of the plurality of short heads which are adjacent to each other in the one direction of arrangement are located such that respective arrays of the recording elements are partly overlapped with each other when viewed from the auxiliary scanning direction.
Preferably, each of the plurality of short heads comprises a plurality of rows of arrays of the recording elements in the auxiliary scanning direction.
Preferably, a plurality of head units in each of which the plurality of short heads are arranged in the one direction of arrangement are arranged in the auxiliary scanning direction.
Preferably, the line head further comprises a selection unit for selecting the recording elements to be used in a joint region of the two of the plurality of short heads which are adjacent each other in accordance with the arrangement pitch and the interval; wherein the driving of the selected recording elements is controlled.